Method and device for determining the knock rating of motor fuels

ABSTRACT

The invention relates to the oil refining and petrochemical industry and concerns, in particular, techniques for determining the knock rating of motor fuels. The proposed method of determining the knock rating of motor fuels involves thermostatic control of a reaction vessel of constant volume, feeding the fuel-air mixture into the vessel, atomization of the mixture under excess pressure and ignition of the mixture. The knock rating is calculated by the knocking intensity which is determined by the value of the signal from a knock sensor installed in the reaction vessel. The proposed apparatus for determining the knock rating of motor fuels comprises a reaction vessel with inlet and outlet valves and a thermostatic controller. A spark plug is installed in the reaction vessel and a knock sensor is arranged opposite the spark plug.

FIELD OF THE INVENTION

The invention relates to area of oil refining and petrochemical industryand concerns in particular techniques of determining of the knock ratingof motor fuels.

BACKGROUND ART

There are known an engine method (Fuel for engines. An engine method fordetermining of octane rating. The USSR State Standard 511-82, ASTM D2700, DIN 51756) and an analyze method (Fuel for engines. An analyzemethod for determining of octane rating. The USSR State Standard8226-82, ASTM D 2699, DIN 51756) for determining of the knock rating offuels including feeding the fuel into a reaction vessel with variabledegree of compression, atomization and ignition of a mixture,determining the knock rating. The method is performed on a one-cylinderengine having variable degree of compression, and the knock rating isexpressed by octane rating numerically equal to percentage of isooctanein such a mixture with normal heptane, knock intensity of which in aone-cylinder engine having variable degree of compression in standardconditions of testing is equivalent to knock intensity of the testedfuel.

The methods based on engine tests correctly, in general, characterizefuels, but exhibit significant drawbacks. Those drawbacks includeconsiderable duration of testing and large consumption of tested fuel.So, testing of one sample of fuel using the engine or research methodslasts for 20 minutes and consumes a tested sample of 300 ml. Intenseexhaust into atmosphere of harmful products of combustion is one ofnegative consequences of the large fuel consumption. Because of largeconsumption of the sample, these methods practically cannot be used fortesting of products, obtained on micro-pilot plants.

Besides, it is very difficult to include these methods into atechnological scheme for on-stream testing of the products or to usethem in a system of automatic control. Furthermore, engines used in thementioned methods are quite expensive and cumbersome.

The closest on technical essence and achieved result is a method basedon initiation of low temperature reaction of gaseous phase oxidation offuel. The method provides thermostatic control of the reaction vessel ofconstant volume up to temperatures 250-350° C., feeding of a portion oftested fuel, mixing it with air contained in the vessel at atmosphericpressure, cool flame oxidation of the formed combustible mixture.Temperature in the reaction vessel increases. The knock rating of motorfuel is characterized by temperature gain and time of achieving ofmaximal temperature. With deterioration of the knock rating of a sample,the temperature is increased, and the time of achieving of maximaltemperature is reduced (U.S. Pat. No. 3,738,810, G01L 23/22, 1973).

Methods and devices based on studying of cool flame processes havenumber of advantages: they are rather inexpensive, application thereofrequires insignificant amount of a sample, they could be easily includedinto a technological system for on-stream testing of products, and theycould also be used in a system of automatic control. They possess,however, one quite essential drawback; testing of fuel is performed inconditions rather far from engine operational conditions. Knockingoccurs in an engine during combustion of fuel, but in the consideredmethod combustion does not occur at all. Using this method there couldbe studied phenomena occurring to fuel during preparation forcombustion, pre-combustion processes. The distinction between conditionsof fuel combustion in an engine and its testing in conditions of coolflame oxidation limits possibilities of the given testing method. Thementioned method gives satisfactory results at testing of homogeneousfuels samples of known composition with insignificant changes, forexample, at the output of the technological system. If fuel compositionis unknown, the results of testing may be unreliable. Besides, employingof this method, it is practically impossible to estimate efficiency ofantiknock additions, since the mechanism of their action is absolutelydifferent, and it is impossible to judge their efficiency using coolflame processes. Therefore, the given method is recommended to use forthe control of mixing processes, in which there are not appliedantiknock additions, in particular, tetraethyl lead (Clinton R. M.,Puzniak T. J. Gulf Research develops continuous-process octane analyzer.Oil and Gas Journal, 1975, 73, No. 16, 77-82).

DISCLOSURE OF THE INVENTION

The invention is based on the problem of providing a method and anapparatus for determining of knock rating of motor fuels in conditionsclose to operational conditions of an internal-combustion engine.

Technical results, that can be achieved with help of the invention, areimproving of reliability of determining of knock rating, widening ofarea of application thereof, in particular, for estimation of efficiencyof antiknock additions, simplifying of determining technique, decreasingof testing duration and consumption of tested fuel, dimensions and costof equipment and also facilitation of inclusion of the apparatus intoflow of the technological system and automatic control system.

This problem is solved by a method of determining a knock rating of amotor fuel fuels, comprising thermostatic control of a reaction vesselof constant volume, feeding the fuel-air mixture into the vessel andatomization of the mixture under excess pressure. The combustiblemixture is then ignited causing knocking and the intensity of theknocking is detected based on a signal from a knock sensor installed inthe reaction vessel.

The method and device proposed according to the present invention allowthe determination of a knock rating of a fuel based on an intensity ofknocking of a combustible mixture ignited in the reactor by a sparkdischarge. Intensity of knocking is a characteristic of the knock ratingof a fuel: the higher the intensity of knocking, the lower the knockrating. Date of intensity of knocking is obtained from a knock sensorinstalled in the reactor.

One of the embodiments of the method of determining the knock rating ofmotor fuels according to the present invention applies an electric-airsystem of thermostatic control for the thermostatic control of thereaction vessel.

Another embodiment of the method of determining the knock rating ofmotor fuels according to the present invention applies anelectric-liquid system for the thermostatic control of the reactionvessel. As a cooling liquid there could be used, for example, distilledwater or ethylene glycol, depending on a choice at development of thetesting procedure, during testing this cooling liquid is in a boilingcondition.

Conditions of testing of a fuel in both embodiments are selecteddepending on knock rating thereof by changing the pressure of air andamount of fuel doze fed into the reaction vessel.

Both for the fuel being tested and for a reference fuel fuel at each airpressure value there is selected a fuel dose ensuring maximum intensityof the knocking. Air pressure is changed until for the tested fuel aknocking intensity accepted as standard for this technique is achieved.Then, and at this value of air pressure the tested fuel is compared withreference fuels. Under action of compressed air the fuel dose issuperseded from fuel system, is atomized and mixed with air in a mixingchamber, it is warmed up to a given temperature by an electrical heaterand is forced into the reaction vessel, where it is ignited by anelectrical spark. Intensity of a knock is evaluated by value of maximalsignal from the knock sensor appearing owing to knock combustion of fuelin the reaction vessel and by time of achieving of this maximum from themoment of discharging of the spark.

For estimation of intensity of knocking there is used a knock sensor. Weused a magnetostrictive knock sensor. Operation of the knock sensor isbased on magnetostrictive effect. Under action of knock waves there isoccurring vibrating deformation of a magnetostrictive core, and in awinding of the core there is inducted electrical voltage proportional toknock intensity. This voltage is registered by an oscillograph or othermeasuring device, and intensity of the knocking is evaluated by valuethereof. The magnetostrictive sensor is not a sole device for measuringof knock intensity. For this purpose it is also possible to use, forexample, a piezo sensor which under action of knock waves also generatesan electrical signal.

Values of temperature of the reaction vessel and fuel-air mixture beforeforcing into the reaction vessel are selected during development of theprocedure and are not changed hereinafter. After combustion of fuel inthe reaction vessel the outlet valve is opened and products ofcombustion are charged out, then the reaction vessel is blown through byclean air and there could be started a new cycle of testing. Controllingof valves, ignition and cycles of testing is performed by a programmer.

The proposed method is realized in an apparatus according to the presentinvention for determining of knock rating of motor fuels containing areaction vessel with inlet and outlet valves and having means ofthermostatic control. In the reaction vessel there are installed a sparkplug and a knock sensor located opposite to the spark plug.

The reaction vessel can be implemented in form of a steel cylinder.

For performing of determining according to the first embodiment there isused an apparatus containing a reaction vessel with electric-air systemof thermostatic control equipped by cooling fins, a thermocouple, aninlet and an outlet valve, an electrical spark plug and a knock sensorinstalled opposite to the spark plug. In order to maintain a requiredthermal mode in the reaction vessel, there are applied means for controland management.

According to the second embodiment there is used an apparatus containinga reaction vessel in form of a steel cylinder equipped by an inlet andan outlet valves, an electrical spark plug and a knock sensor installedopposite to the spark plug. In order to maintain a required thermal modeof the reaction vessel there is applied a system for electric-liquidthermostatic control consisting of a cooling jacket around the reactionvessel, a condenser of vapors of the cooling liquid, a heater, ameasuring glass and a control thermometer.

Distilled water or ethylene glycol could be, for example, applied in theapparatus as a cooling liquid, depending on selection in course of thedevelopment of the testing procedure, and during the testing the coolingliquid is in a boiling condition.

Except the system of thermostatic control, the apparatuses according toboth embodiments are identical.

A method and an apparatus proposed according to the present inventionallow determination of the knock rating of a fuel by intensity ofknocking of the combustible mixture ignited in a reactor by a sparkdischarge. Intensity of knocking is a characteristic of knock rating ofthe fuel: the higher the intensity of knocking, the lower the knockrating. Data concerning intensity of knocking is received from a knocksensor installed in the reactor.

The advantages specified above and the peculiarities of the presentinvention will now be described with references to the preferredembodiments of the invention, with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The method and the apparatus are explained with reference to thefollowing drawings:

FIG. 1 is a schematic view of an apparatus with an electric-air systemof thermostatic control.

FIG. 2 is a schematic view of an apparatus with an electric-liquidsystem of thermostatic control.

FIG. 3 is diagrams of knock characteristics of normal heptane in testingat a pressure of 3 atm. and at temperatures of 150, 210 and 265° C.

FIG. 4 is diagrams of knock characteristics of isooctane and normalheptane in testing at a pressure of 3 atm. and at a temperature of 210°C.

FIG. 5 is a diagram of knock characteristics of isooctane in testing ata pressure of 10 atm. and at a temperature of 305° C.

FIG. 6 is a diagram of knock characteristics of pure mixture ofisooctane with normal heptane using of antiknock addition (tetraethyllead).

FIGS. 3-6 and the Table represent signals from a magnetostrictive knocksensor at combustion of various fuels. The experiments were carried outin a steel cylindrical reactor with internal diameter of 60 mm andlength 145 mm. The temperatures were determined with help of athermocouple installed inside the reactor.

BEST METHOD OF CARRYING OUT THE INVENTION

The apparatus is based on a steel cylindrical reactor 1 withthermostatic control having internal diameter of 40-100 mm, length of60-200 mm (see FIG. 1 and FIG. 2). Temperature of the reactor ismaintained with help of an electric-air system of thermostatic control(FIG. 1) or an electric-liquid system of thermostatic control (FIG. 2).

The electric-air system of thermostatic control (FIG. 1) comprises aheater 2, a thermocouple 3, cooling fins 4 ventilated by a fan and adevice 10 for controlling and adjustment of the reactor temperature.

The electric-liquid system of thermostatic control (FIG. 2) consists ofa cooling jacket 42, around of the reactor 1, a condenser of vapors ofcooling liquid 43, a heater 44, a control thermometer 50 and a measuringglass 11. Other details of both embodiments of the apparatus 20 areidentical. On the top cover of the reactor there are installed an inletand an outlet valves 5 and 7 and a spark plug 6 fed by a block 21. Onthe bottom cover there is installed a knock sensor 8 connected with arecording apparatus 9.

A necessary amount of tested or reference fuel is fed through thecrane-switch 31, is installed by a dosing element 13 and is entered intothe mixer 19 for forming of fuel-air mixture which is fed through theheater 20 into the reactor. Temperature of the mixture in range of500-200° C. is controlled and managed with help of a thermocouple 29 anda regulator 30.

Air is fed into the mixer and reactor through an air line comprising acapacity 25, a reducer 24, a receiver 23, valves 14 and 17, and also asmall cylinder 16 for blasting through the reactor. The capacity 25could be implemented in form of either a compressed air cylinder (150atm.) or a cylinder pumped up with air by its own compressor. Thecylinder 16 has capacity of 0.2-1 1., the receiver 23 is of 2-10 1.capacity, air is fed into the cylinder 16 through the reducer 27 set upfor pressure 2-3 atm. and connected with an air line before the valve17, and air is output through the valve 28 installed after the valve 17.

Tested and reference fuels are placed in tanks 32 and flow by gravitytherefrom through the crane-switch 31.

Testing of the fuels is performed as follows. Initially the inlet andoutlet valves 5 and 7 are open, valves 14, 17 and 28 are closed. Air andfuel are not fed into the reactor, but dosing element 13 connected bythe crane 31 with one of tanks 32 is filled by fuel from this tank.After establishing a desired temperature of the reactor and pressure inthe operative receiver 23 the outlet valve 7 is closed and the valve 17is opened simultaneously. Thus, under pressure of air the valve 14 ispassed to the bottom position and the dosing element becomes isolatedfrom the fuel line and connected to the air line. There is performedinjection of the fuel-air mixture into the reactor, at the same time thefuel is atomized, evaporates, mixes up with air, is heated up and formsa combustible mixture. At a required interval of time the valves 5 and17 are closed simultaneously, and the valve 28 is opened, and electricalspark of a spark plug 6 ignites the combustible mixture.

In result of combustion of the mixture, there is formed a knock, theintensity of which depends on knock rating of tested fuel. An electricsignal from the knock sensor 8 comes into the recording apparatus 9,where there are recorded parameters thereof: maximal level of the signalformed due to knock combustion of the fuels in the reactor and time ofachieving of this maximum from the moment of discharging of the spark.During development of the procedure there should be solved a questionwhat should be taken into consideration at comparison of tested fuelwith the standards: either maximal level of the signal, or rate of thismaximal level to time of achieving thereof.

After combustion of the mixture the outlet valve 7 is opened, throughwhich there is performed exhaust of combustion products from thereactor, time of opening of the outlet valve is 0.5-2 sec. after sendingof voltage onto the spark plug. In 1-3 sec. after opening of the outletvalve 7 the inlet valve 5 is opened and there is performed blastingthrough of the reactor by clean air from the cylinder 16. Duration ofblasting through the reactor is 1-3 sec. The valve 28 is closed.Normally the valve 28 is in a closed position, therefore, there ismaintained a constant required pressure in the cylinder 16. The inletand outlet valves 5 and 7 remain open. On this the cycle is completed.

Because of the pressure in the air line drops up to atmosphericpressure, valve 14 of the dosing element passes into the top position,the dosing element become disconnected from the air line and connectedto the fuel line.

A new cycle begins with filling of the dosing element with fuel, thus,due to an open position of valves 5 and 7, there is atmospheric pressurein the dosing element. Duration of a pause between cycles is establishedby practical consideration during development of the procedure.

Controlling of the valves, ignition and testing cycles is performed bythe programmer 22. Process of testing of fuels is basically similar tothe standard technique of determining of octane ratings with using ofengine testing systems.

Dimensions of the reactor and other units could be finally determinedduring development of the apparatus design, being guided by thenecessity of achievement of optimum testing results.

In a process of development of a procedure there are selected a thermalmode, knocking intensity, at which the tested sample is compared withthe standards, time intervals between operations.

Pressure of air for each tested sample, depending on its knock rating,is selected in process of testing, so that knock intensity would notfall outside the limits of values accepted for the technique. Thus, foreach value of air pressure there is selected such a dose of fuel, whichprovides maximal knocking intensity.

The present invention is further illustrated by the following examples.

EXAMPLE 1

On FIG. 3 there are shown results of testing performed on normal heptaneat constant pressure of 3 atm., but at various temperatures: 150, 210and 265° C. With increasing of temperature, combustion become moresevere, and signal from the knock sensor sharply increases.

EXAMPLE 2

In order to be convinced, that we observe just a knock, a test inidentical conditions was performed on isooctane and normal heptane. Itis known, that the isooctane differs from normal heptane by improvedknock rating only. On FIG. 4 there are presented records of oscillographindications, corresponding to the results of testing of isooctane andnormal heptane. As it is clear from FIG. 4, the curve--isooctanesignal--has a smooth form, while the signal from normal heptane hassharp high peak--obvious affirmation of a knock.

EXAMPLE 3

The method and the apparatus allow to achieve knock effect also attesting of isooctane, however, at more severe conditions (under airpressure of 10 atm. and at temperature 305° C.). The obtained curve isshown on FIG. 5.

EXAMPLE 4

With the purpose of studying of data concerning changing of knockintensity depending on fuel composition, there were performed serialtesting of fuels with following content of isooctane and normal heptane(%): 67:33; 75:25; 85:15; 100:0.

                  TABLE                                                           ______________________________________                                        (Test conditions: pressure 3 atm., temperature - 260° C.)              ______________________________________                                        Isooctane content in                                                                          67     75       85   100                                      mixture with normal                                                           heptane                                                                       Knocking intensity (in                                                                        5.8    4.8      4.4  1.3                                      conditional units - value                                                     H in oscillograph record)                                                     ______________________________________                                    

As there is evident from the data presented in the Table, the knockintensity is reduced in accordance with increasing of isooctane contentin a tested sample, in other words, method allows to judge withconfidence the knock rating of fuel of mixed composition.

EXAMPLE 5

For achieving the data concerning changing of knocking intensity of fuelin result of application of antiknock additions, there were testedmixtures of 75% of isooctane with 25% of normal heptane in pure stateand with additive of tetraethyl lead (TEL) in the ratio of 1 ml. of TELfor 1 1. of fuel. As it is visible on FIG. 6, in contrast to the puremixture, the knock curve of the fuel with TEL has a cut off peak. Thus,the method allows to estimate knock rating of fuels containing antiknockadditions.

Fuel consumption for one measurement depending on pressure of air is0.05-0.3 ml. Therefore, for fulfillment, for example, of 20measurements, maximal sample consumption will be not more than 6 ml.Owing to such insignificant samples consumption, all difficultiesrelated to maintenance of testing on micro-pilot plants could beovercome.

When working with a model of the apparatus with manual control andtesting results registration, the complete cycle of one measurementcomprised no more than 30 sec. Operating an industrial type apparatushaving automated control and testing results registration, this time canbe reduced up to several seconds.

INDUSTRIAL APPLICABILITY

The proposed method and apparatus can be used in oil refining andpetrochemical industry and in analytical practice for research andtesting works for determining of knock rating of fuels of variouscomposition, including compositions containing antiknock additions andvarious components. The proposed apparatus supplied by a programmer,could be easily included in flow of a technological system and in anautomatic control system. Other opportunities and advantages of theclaimed invention will be apparent to those skilled in the art.

We claim:
 1. A method of determining a knock rating of a sample of motorfuel comprising the steps of:thermostatically controlling a reactionvessel of constant volume; feeding an atomized mixture of the sample offuel and air into the reaction vessel at a predetermined excesspressure, wherein the predetermined excess pressure and the temperatureof the reaction vessel are controlled to ensure maximal knockingintensity; igniting the fuel-air mixture in the reaction vessel;detecting, for each ignition, a knocking intensity of the fuel-airmixture; and determining, for each ignition, the knock rating of thesample of fuel based on a magnitude of the knocking intensity of thefuel-air mixture.
 2. A method according to claim 1, wherein anelectric-air thermostatic control system is employed in thermostaticallycontrolling the reaction vessel.
 3. A method according to claim 1,wherein an electric-liquid thermostatic control system is employed inthermostatically controlling the reaction vessel.
 4. A method accordingto claim 3, wherein one of distilled water and ethylene glycol isemployed as a cooling liquid in the electric-liquid thermostatic controlsystem.
 5. A method according to claim 1, wherein fuel testingconditions are selected depending on a predicted knock rating of thefuel by varying the predetermined excess pressure and a dose amount offuel fed into the reaction vessel.
 6. An apparatus for determining aknock rating of motor fuel, comprising:a reaction vessel; thermostaticcontrol means for maintaining a predetermined temperature within thereaction vessel; an inlet valve and an outlet valve mounted on thereaction vessel; a spark plug mounted within the reaction vessel; aknock sensor mounted within the reaction vessel opposite to the sparkplug; means for determining a knock rating of fuel ignited in thereaction vessel based on a comparison of a magnitude of a signal outputfrom the knock sensor to a value corresponding to a reference fuel. 7.An apparatus according to claim 6, wherein the thermostatic controlmeans comprise an electric heater and an air cooler.
 8. An apparatusaccording to claim 6, wherein the thermostatic control means comprise acooling jacket, a heater, a condenser for condensing vapor formed by thecooling liquid, a measuring glass and a control thermometer.
 9. Anapparatus according to claim 6, wherein one of distilled water ethyleneglycol is used as a cooling liquid.
 10. An apparatus according to claim6, wherein the reaction vessel is formed as a steel cylinder.